Internal combustion engines, such as multi-cylinder diesel engines, typically include a crankshaft, a camshaft and a rocker arm shaft. The crankshaft is connected with a plurality of piston rods, which in turn are connected with a plurality of corresponding pistons. Reciprocating movement of the pistons within corresponding combustion cylinders causes rotation of the crankshaft.
Generally, the crankshaft is interconnected with the camshaft via a gear set and thereby rotatably drives the camshaft during operation. The camshaft includes a plurality of cams, with each cam being associated with an inlet valve, and an exhaust valve or a fuel injector valve. More particularly, the rocker arm shaft carries a plurality of rocker arms, with each rocker arm having a roller follower, which engages a corresponding cam on the camshaft. Rotation of the camshaft causes oscillatory pivotal movement of the rocker arms about the rocker arm shaft.
In overhead cam engines, rocker arm stands typically are built into the cylinder head casting. The rocker arm shaft it then secured to the stands, the rocker arms pivoting around the stationary rocker arm shaft. Although the rocker arms pivot through a relatively small pivoting angle about the stationary rocker arm shaft, this pivoting may not be sufficient to allow the formation of a hydrodynamic oil film between the rocker arms and the rocker arm shaft. As a result, the friction between the rocker arms and the rocker arm shaft may be relatively high, causing increased wear or spalling between the rocker arms and the rocker arm shaft. Additionally, the movement of the rocker arm shaft and rocker arms may likewise cause damage to the rocker arm stands themselves. Excessive wear can cause inefficient operation of the engine, necessitating replacement of the entire cylinder head casting.
In order to minimize wear, various arrangements have been proposed to increase lubrication and/or reduce friction between the rocker arms and the rocker arm shaft. These proposals are often not entirely effective, or are of relatively high cost to facilitate. For example, it is known to oscillate a rocker arm shaft through a small rotational angle using a rack and pinion arrangement in order to change the eccentricity of the rocker arms relative to the rocker arm shaft. The arrangement disclosed in U.S. Pat. No. 4,718,379 to Clark provides a roller bearing pivot assembly between the shaft and the rocker arm. The retrofit roller bearing pivot assembly about the top of a spacer member, which forms the rocker arm shaft, the assembly extending along the sides of the spacer member. Of these proposals, however, neither repairs prior damage nor wear.
The present disclosure is directed to overcoming one or more of the problems as set forth above.